A continuation of studies on the biosynthesis of fatty acids, cholesterol and carotenes is proposed. The emphasis in these studies will, however, be placed on the biosynthesis of fatty acids. Attempts will be made to develop a new method of separation of the nonidentical half-molecular weight subunits of pigeon and rat liver fatty acid synthetases. Antisera to each subunit will then be prepared. A reinvestigation of the properties of each subunit will be carried out and determinations will be made of the number and identity of N-terminal and carboxy-terminal amino acids. Studies will also continue on the purification, properties and regulation of the enzymes that bring about the interconversion of apo- and holofatty acid synthetases. Related studies will be carried out to determine whether significant changes in the specific activity of the fatty acid synthetase occur as a result of changes in nutritional or hormonal state of a animal. Answers to this question will be obtained by immunotitration of enzyme with monospecific antiserum. Studies with isolated hepatocytes will be directed towards the identification of the mechanism by which glucagon and insulin bring about a change in acetyl-CoA carboxylase and fatty acid synthetase activities. A final study will be directed towards the isolation and purification of the mRNA for the fatty acid synthetase and the translation of this mRNA in a cell-free wheat germ system. Studies on cholesterol synthesis will be devoted largely to the isolation and purification of enzyme systems that interconvert enzymatically active and inactive beta-hydroxy-beta-methylglutaryl coenzyme A reductase. Those on carotene synthesis will be concerned primarily with the isolation and purification of enzymes that convert isopentenyl pyrophosphate to acyclic and cyclic carotenes.